https://search.dev.ndltd.org/etd/lincoln/oai:researcharchive.lincoln.ac.nz:10182/15889
type: CreativeWork
name: Effect of replacing nitrogen fertiliser with gibberellic acid on response of perennial ryegrass and white clover pasture : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
description: New Zealand dairy farms are no longer allowed to use high rates of nitrogen (N)-based fertiliser to achieve maximum pasture production due to the associated losses of N through nitrate leaching and nitrous oxide emissions. Gibberellic acid (GA), a naturally occuring phytohormone, has shown in short term studies, to increase, then reduce pasture yield when applied exogenously. The purpose of this research was to compare the long term effects of substituting N fertiliser with GA on a perennial ryegrass (Loliume perenne, PRG) and white clover (Trifolium repens, WC) pasture. A twelve-month, cut and carry plot trial explored dry matter (DM) production, botancial composition, ryegrass tiller size and density and forage nutritive value. To test these results, several treatment regimens were compared in a grazing trial with dairy cows which explored milk production and N excretion. Using a randomised block design with ten treatment regimens and four blocks, GA was applied to PRG and WC pasture plots to evaluate the timing and frequency of GA use in spring and autumn. Gibberellic acid replaced N fertiliser (once, twice or three times) in combinations of early (August and February), delayed (September and March) or late (October and April) applications. The control treatment was N fertiliser applied at 250 kg N/ha/y, the positive control was GA applied with every application of N fertiliser (80 g GA/ha/y + 250 kg N/ha/y) and the untreated control had no N fertiliser or GA. The first of ten applications occurred in August 2012 and the last in May 2013. Measurements included DM yield, botanical separation, tiller counts and nutrient content. Annual herbage yield was 14.6, 18.3 and 18.3t DM/ha/y (P<0.001) for the three controls (untreated, GA+N fertiliser and N fertiliser, respectively). By replacing N applications with GA, herbage yield declined showing a positive relationship between annual N fertiliser application and DM yield. There was no effect of GA on annual yield, nor w…
abstract: New Zealand dairy farms are no longer allowed to use high rates of nitrogen (N)-based fertiliser to achieve maximum pasture production due to the associated losses of N through nitrate leaching and nitrous oxide emissions. Gibberellic acid (GA), a naturally occuring phytohormone, has shown in short term studies, to increase, then reduce pasture yield when applied exogenously. The purpose of this research was to compare the long term effects of substituting N fertiliser with GA on a perennial ryegrass (Loliume perenne, PRG) and white clover (Trifolium repens, WC) pasture. A twelve-month, cut and carry plot trial explored dry matter (DM) production, botancial composition, ryegrass tiller size and density and forage nutritive value. To test these results, several treatment regimens were compared in a grazing trial with dairy cows which explored milk production and N excretion. Using a randomised block design with ten treatment regimens and four blocks, GA was applied to PRG and WC pasture plots to evaluate the timing and frequency of GA use in spring and autumn. Gibberellic acid replaced N fertiliser (once, twice or three times) in combinations of early (August and February), delayed (September and March) or late (October and April) applications. The control treatment was N fertiliser applied at 250 kg N/ha/y, the positive control was GA applied with every application of N fertiliser (80 g GA/ha/y + 250 kg N/ha/y) and the untreated control had no N fertiliser or GA. The first of ten applications occurred in August 2012 and the last in May 2013. Measurements included DM yield, botanical separation, tiller counts and nutrient content. Annual herbage yield was 14.6, 18.3 and 18.3t DM/ha/y (P<0.001) for the three controls (untreated, GA+N fertiliser and N fertiliser, respectively). By replacing N applications with GA, herbage yield declined showing a positive relationship between annual N fertiliser application and DM yield. There was no effect of GA on annual yield, nor w…
author: Miller, Melanie Elizabeth
language: en
keywords: urea, nitrogen fertiliser, gibberellic acid, ProGibb®SG, perennial ryegrass, Lolium perenne, white clover, Trifolium repens, pasture management, fertiliser management, ANZSRC::300407 Crop and pasture nutrition, ANZSRC::300411 Fertilisers (incl. application), ANZSRC::410404 Environmental management
license: https://creativecommons.org/licenses/by-nd/4.0/
date published: 2022
date modified: 2026-07-24T02:50:42Z
provider: Lincoln University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Lincoln University

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property ID: Handle
value: https://hdl.handle.net/10182/15889